Particle detector

ABSTRACT

There is provided a particle detector that can increase a detection sensitivity to fluorescence emitted from biogenic particles. A particle detector for detecting biogenic particles includes a substrate having a principal surface and configured to collect the biogenic particles on the principal surface, a light emitting element configured to irradiate particles collected on the principal surface with excitation light, and a light receiving element configured to receive fluorescence emitted from the particles when the particles are irradiated with the excitation light from the light emitting element. An optical axis of the Fresnel lens and a ray direction of the excitation light intersect with each other. The principal surface is a mirror surface.

TECHNICAL FIELD

The present invention relates to a particle detector, and moreparticularly, to a particle detector that detects biogenic particles.

BACKGROUND ART

There has hitherto been proposed an apparatus that measures the numberof microorganisms existing in a specimen by staining the specimen with afluorescent staining reagent and irradiating the specimen withexcitation light to emit fluorescence (see, for example, JapaneseUnexamined Patent Application Publication No. 2008-145276 (PTL 1)). Inthe apparatus disclosed in Japanese Unexamined Patent ApplicationPublication No. 2008-145276 (PTL 1), the excitation light applied to thespecimen and the fluorescence emitted from the specimen are coaxial witheach other, the fluorescence is caused to arrive via a filter at anoptical system for receiving the fluorescence, and the excitation lightis removed by the filter.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2008-145276

SUMMARY OF INVENTION Technical Problem

In the method for detecting fluorescence from biogenic particles byirradiating the particles with excitation light, when the excitationlight reaches a light receiving unit, it becomes noise and decreases thedetection sensitivity to fluorescence in the light receiving unit. Thereis a limit to separation of the excitation light by only the filter, andsufficient detection sensitivity to fluorescence is sometimes notobtained. Also, since the filter needs to be additionally provided, thesize and cost of the apparatus increase.

The present invention has been made in view of the above problems, and amain object of the invention is to provide a particle detector that canimprove a detection sensitivity to fluorescence emitted from biogenicparticles.

Solution to Problem

A particle detector according to the present invention detects biogenicparticles, and includes a collecting member having a principal surfaceand configured to collect the biogenic particles on the principalsurface, a light irradiation unit configured to irradiate the particlescollected on the principal surface with excitation light, and a lightreceiving unit configured to receive fluorescence emitted from theparticles when the particles are irradiated with the excitation lightfrom the light irradiation unit. An optical axis of the light receivingunit and a ray direction of the excitation light intersect with eachother. The principal surface is a mirror surface.

In the particle detector, preferably, the fluorescence is specularlyreflected by the principal surface.

In the particle detector, preferably, the light irradiation unitincludes an edge-emitting semiconductor laser element, and thesemiconductor laser element has a multilayer structure including a lightemitting layer, and is disposed such that a stacking direction of themultilayer structure is parallel to the principal surface.

In the particle detector, preferably, the light receiving unit includesa light collecting lens, and the light collecting lens contains amaterial that absorbs the excitation light.

In the particle detector, preferably, the light collecting lens is aFresnel lens.

In the particle detector, preferably, the following relationship isestablished:T=(B/cos θ+L)/2 tan θwhere θ represents an incident angle of the excitation light on theprincipal surface, L represents a diameter of the light collecting lens,T represents a distance between the light collecting lens and theprincipal surface, and B represents a diameter of the excitation light.

Advantageous Effects of Invention

According to the particle detector of the present invention, it ispossible to increase the detection sensitivity to fluorescence emittedfrom biogenic particles.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating an appearance of a particledetector according to an embodiment.

FIG. 2 is a perspective view illustrating an exploded state of theparticle detector illustrated in FIG. 1.

FIG. 3 is an exploded perspective view illustrating a detailedconfiguration of the particle detector.

FIG. 4 is a cross-sectional view of the particle detector.

FIG. 5 schematically illustrates the behavior of light in an opticalsystem included in the particle detector.

FIG. 6 schematically illustrates light reflection on a principal surfaceof a substrate.

FIG. 7 schematically illustrates a cross section of a Fresnel lens.

FIG. 8 is a graph showing filter characteristics of absorbent.

FIG. 9 schematically illustrates radiation characteristics of lightemitted from a semiconductor laser element.

FIG. 10 schematically illustrates an arrangement of the semiconductorlaser element based on the radiation characteristics of laser light.

FIG. 11 is a first schematic view illustrating an arrangement of theFresnel lens relative to the substrate.

FIG. 12 is a second schematic view illustrating an arrangement of theFresnel lens relative to the substrate.

FIG. 13 is a third schematic view illustrating an arrangement of theFresnel lens relative to the substrate.

FIG. 14 is a flowchart showing a flow of operations of the particledetector.

FIG. 15 shows the time change of a fluorescence spectrum of Penicilliumbefore and after heat treatment.

FIG. 16 shows a fluorescence spectrum of fluorescence-emitting dustbefore heat treatment.

FIG. 17 shows a fluorescence spectrum of the fluorescence-emitting dustafter heat treatment.

FIG. 18 illustrates an exemplary appearance of an air purifier includingthe particle detector.

FIG. 19 is a block diagram showing an exemplary functional configurationof the air purifier.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described below withreference to the drawings. In the following drawings, the same orcorresponding parts are denoted by the same reference numerals, anddescriptions thereof are not repeated.

[Overall Configuration of Particle Detector]

FIG. 1 is a perspective view illustrating an appearance of a particledetector 1 according to the embodiment. FIG. 2 is a perspective viewillustrating an exploded state of the particle detector 1 of FIG. 1.FIG. 3 is an exploded perspective view illustrating a detailedconfiguration of the particle detector 1. The particle detector 1 of theembodiment is an apparatus that detects biogenic particles such aspollen, microorganisms, and mold.

The particle detector 1 of the embodiment includes an upper cabinet 2serving as a first housing, and a lower cabinet 5 serving as a secondhousing. The upper cabinet 2 is shaped like a substantially rectangularflat plate. The lower cabinet 5 is shaped like a substantiallyrectangular parallelepiped container having a bottom and opening in onedirection. The upper cabinet 2 and the lower cabinet 5 are assembledsuch that the upper cabinet 2 closes the opening of the lower cabinet 5like a lid, so that a hollow cabinet having an outer shape like asubstantially rectangular parallelepiped is formed.

Devices that constitute the particle detector 1, such as a collectingunit 60, an excitation optical system 20, a light receiving opticalsystem 30, and a cleaning unit 96, except for a fan 92, are contained inthe cabinet. As an example, the cabinet has a size of 60 mm×50 mm(length and width of the upper cabinet 2)×30 mm (height).

A collecting cylinder 4 serving as a cylindrical member is providedintegrally with the upper cabinet 2. The collecting cylinder 4 is shapedlike a hollow cylinder, and extends from the upper cabinet 2 into theinside of the particle detector 1 while being attached at one end to alower surface of the upper cabinet 2. The upper cabinet 2 has anintroducing portion 3 that penetrates a part of the upper cabinet 2 in athickness direction. The outside of the particle detector 1 and theinside of the collecting cylinder 4 communicate with each other via theintroducing portion 3. The collecting cylinder 4 is provided to surrounda below-described electrostatic probe 62. Air containing particles isintroduced from the introducing portion 3 into the collecting cylinder4. The collecting cylinder 4 guides the air containing particles towarda substrate 10 positioned opposed to the electrostatic probe 62.

A fan 92 is attached to an outer side of a bottom surface of the lowercabinet 5. The bottom surface of the lower cabinet 5 to which the fan 92is attached has an aperture. This aperture opens to include an areaopposed to the collecting cylinder 4 and an area opposed to abelow-described brush 97, and is continuously formed by the area opposedto the collecting cylinder 4 and the area opposed to the brush 97.

The fan 92 can be rotationally driven in a forward direction and areverse direction. When the fan 92 is driven in the forward direction,air in an inner space of the particle detector 1 is exhausted out of theparticle detector 1 through the fan 92. When the fan 92 is driven in thereverse direction, air outside the particle detector 1 is introducedinto the inner space of the particle detector 1 through the fan 92. Thefan 92 is used for collection of particles into the particle detector 1,cooling of the particles after heating, and cleaning of the substrate 10for collecting the particles. This reduces the size and cost of theparticle detector 1.

The particle detector 1 includes a collecting unit 60. The collectingunit 60 collects particles contained in air onto a principal surface 11of a substrate 10 serving as a collecting member. The collecting unit 60includes a collection power-supply circuit 61 formed by a high-voltagepower supply, and an electrostatic probe 62 serving as a dischargeelectrode. The substrate 10 has the principal surface 11. The substrate10 is provided as a collecting member that collects, onto the principalsurface 11, particles in which biogenic particles and powder dust, suchas lint of chemical fiber, are mixed.

The substrate 10 is formed by a silicon flat plate. On the principalsurface 11 of the substrate 10 for adsorbing particles, a conductivetransparent coating is provided. The substrate 10 is not limited tosilicon, but may be formed of glass, a ceramic material, or metal. Thecoating is not limited to the transparent coating, but, for example, ametallic coating may be provided on the surface of the substrate 10formed of a ceramic material. When the substrate 10 is formed of metal,it is unnecessary to form a coating on the surface of the substrate 10.As long as the substrate 10 is a silicon substrate, the material itselfis inexpensive, and it is easy to conduct mirror finishing on theprincipal surface 11 and to form the conductive coating on the principalsurface 11.

The collection power-supply circuit 61 is provided as a power supplypart that produces a potential difference between the substrate 10 andthe electrostatic probe 62. The electrostatic probe 62 extends from thecollection power-supply circuit 61, penetrates the collecting cylinder4, and reaches an inner portion of the collecting cylinder 4. Thesubstrate 10 is disposed opposed to the electrostatic probe 62. In thisembodiment, the electrostatic probe 62 is electrically connected to apositive electrode of the collection power-supply circuit 61. Thecoating provided on the principal surface 11 of the substrate 10 iselectrically connected to a negative electrode of the collectionpower-supply circuit 61.

The electrostatic probe 62 may be electrically connected to the positiveelectrode of the collection power-supply circuit 61, and the coatingprovided on the substrate 10 may be connected to a ground potential.Alternatively, the electrostatic probe 62 may be electrically connectedto the negative electrode of the collection power-supply circuit 61, andthe coating provided on the substrate 10 may be electrically connectedto the positive electrode of the collection power-supply circuit 61.

When the fan 92 is driven in the forward direction, air in the cabinetof the particle detector 1 is exhausted, and simultaneously, air outsidethe cabinet is introduced toward the substrate 10 through the collectingcylinder 4. At this time, when a potential difference is producedbetween the electrostatic probe 62 and the substrate 10 by thecollection power-supply circuit 61, particles in the air are positivelycharged around the electrostatic probe 62. The positively chargedparticles are moved to the substrate 10 by electrostatic force, areadsorbed by the conductive coating provided on the principal surface 11of the substrate 10, and are thereby collected on the substrate 10.

In this way, in the particle detector 1 of the embodiment, particles arecollected on the substrate 10 by charge collection utilizingelectrostatic force. In this case, it is possible to reliably hold theparticles on the substrate 10 during detection of the particles and toeasily remove the particles from the substrate 10 after detection of theparticles. By using the needle-like electrostatic probe 62 as adischarge electrode, the charged particles can be adsorbed on thesurface of the substrate 10 opposed to the electrostatic probe 62 and inan extremely narrow region corresponding to an irradiation region of abelow-described light emitting element. This allows adsorbedmicroorganisms to be efficiently detected in a fluorescence measuringstep.

The particle detector 1 includes an excitation optical system 20 and alight receiving optical system 30. The excitation optical system 20functions as a light irradiation unit that irradiates particlescollected on the principal surface 11 of the substrate 10 withexcitation light. The light receiving optical system 30 functions as alight receiving unit that receives fluorescence emitted from theparticles with irradiation with excitation light from the excitationoptical system 20. The excitation optical system 20 and the lightreceiving optical system 30 constitute a fluorescence detection unitthat detects fluorescence emitted from the particles collected on thesubstrate 10. The excitation optical system 20 and the light receivingoptical system 30 carry out measurement of fluorescence emitted from theparticles collected on the substrate 10 before and after the particlesare heated.

The excitation optical system 20 includes a light emitting element 21serving as a light source, an exciting portion frame 22 and 23, a lightcollecting lens 24, and a lens presser 25. As the light emitting element21, a semiconductor laser element for emitting blue laser light with awavelength of 405 nm is used. Alternatively, an LED (Light EmittingDiode) may be used as the light emitting element 21. The wavelength oflight emitted from the light emitting element 21 may be in anultraviolet range or a visible range as long as the light excitesbiogenic particles to cause fluorescence emission from the particles.

The light receiving optical system 30 includes a metallic noise shield36, a light receiving element 34, a light-receiving portion frame 33, aFresnel lens 32, and a lens presser 31. As the light receiving element34, a photodiode or an image sensor is used, for example. Between thelight receiving element 34 and the noise shield 36, an amplifyingcircuit 55 is disposed to amplify signals detected by the lightreceiving element 34.

A cleaning unit 96 removes particles from the principal surface 11 ofthe substrate 10. The cleaning unit 96 includes a brush 97 serving as acleaner, and a brush fixing portion 98. The cleaning unit 96 is fixedlysupported on the collection power-supply circuit 61.

The brush 97 is formed by a fiber assembly having conductivity. Forexample, the brush 97 is formed of carbon fiber. The fiber diameter ofthe fiber assembly that forms the brush 97 is preferably within a rangeof 0.05 to 0.2 mm. One end of the brush 97 is supported by the brushfixing portion 98, and the other end thereof is a free end hanging fromthe brush fixing portion 98. As the brush 97 moves relative to thesubstrate 10 with the free end of the brush 97 being in contact with theprincipal surface 11 of the substrate 10, particles are removed from thesubstrate 10.

The collector for removing particles from the substrate 10 is notlimited to the brush 97. For example, the collector may be a wipershaped like a flat plate in contact with the principal surface 11 of thesubstrate 10, or a nozzle for jetting air toward the principal surface11 of the substrate 10.

The particle detector 1 further includes a holding member 80 on whichthe substrate 10 is mounted and held, and a driving unit 70 serving as amoving mechanism for moving the substrate 10. The driving unit 70includes a rotary motor 71 to be rotationally driven, a motor holder 72for holding the rotary motor 71, and a motor presser 73 for positioningthe rotary motor 71.

The holding member 80 includes a rotary base 81. The rotary base 81 isformed of a resin material having low thermal conductivity. The rotarybase 81 has a shaft hole 82. By inserting an output shaft of the rotarymotor 71 in the shaft hole 82, the rotary motor 71 and the rotary base81 are coupled to each other. Upon driving of the rotary motor 71, therotary base 81 rotates (forward, in reverse) about the position of theshaft hole 82.

The holding member 80 includes an arm 83 extending away from a rotationshaft of the rotary base 81. The arm 83 extends in a radial directionorthogonal to the rotation shaft of the rotary base 81, and has aframe-shaped portion at a distal end thereof. The frame-shaped portionhas a shape such as to be able to receive the substrate 10. Thesubstrate 10 is mounted on the holding member 80 by being received inthe frame-shaped portion provided at the distal end of the arm 83.

The particle detector 1 includes a heater 91 serving as a heating unit.The heater 91 is disposed on a back surface of the substrate 10, andheats particles collected on the principal surface 11 of the substrate10. The heater 91 is stuck on the back surface of the substrate 10. Theheater 91 moves together with the substrate 10 during rotation of therotary base 81. To the heater 91, a plurality of lines, including apower supply line to the heater 91 and a signal line of a sensorincorporated in the heater 91, are connected. These lines are led out ofthe cabinet of the particle detector 1.

A position sensor 76 is disposed on a side surface of the lower cabinet5. The substrate 10 is moved in the cabinet of the particle detector 1by rotation of the rotary motor 71. The position sensor 76 is providedto detect the current position of the substrate 10.

[Structure of Fluorescence Detecting Unit]

FIG. 4 is a cross-sectional view of the particle detector 1. FIG. 5schematically illustrates the behavior of light in the optical systemincluded in the particle detector 1. FIG. 6 schematically illustrateslight reflection on the principal surface 11 of the substrate 10.

As described above, the excitation optical system 20 for irradiating theprincipal surface 11 of the substrate 10 with excitation light includesthe light emitting element 21 and the light collecting lens 24.Excitation light EL produced by the light emitting element 21 formed bya semiconductor laser element is collected through the light collectinglens 24, and is applied onto an excitation-light irradiation region 104on the principal surface 11 of the substrate 10. The excitation light ELobliquely enters the principal surface 11 of the substrate 10. In FIGS.5 and 6, a one-dot chain line denoted by symbol OD1 represents a raydirection of the excitation light EL. Here, the ray direction refers toa direction in which a luminous flux component of light (in this case,excitation light EL) travels. In other words, the ray direction OD1 ofthe excitation light EL is an optical axis of the excitation opticalsystem 20.

The principal surface 11 of the substrate 10 is a mirror surface. Theexcitation light EL incident on the principal surface 11 at an incidentangle θ is specularly reflected by the principal surface 11. Lightobtained by regular reflection of the excitation light EL on theprincipal surface 11 forms reflected light RL. In FIGS. 5 and 6, aone-dot chain line denoted by symbol OD2 represents a ray direction ofthe reflected light RL. Since the excitation light EL is obliquelyincident on the principal surface 11 of the substrate 10, the reflectedlight RL specularly reflected by the principal surface 11 is alsoobliquely reflected by the principal surface 11.

In FIG. 6, a one-dot chain line denoted by symbol A represents anoptical axis of the light receiving optical system 30, that is, anoptical axis of the Fresnel lens 32. The ray direction OD1 of theexcitation light EL and the ray direction OD2 of the reflected light RLintersect the optical axis A. The ray directions OD1 and OD2 are at anangle to the optical axis A. The ray directions OD1 and OD2 are at anangle to an extending direction of the principal surface 11 of thesubstrate 10. FIG. 6 also shows a distance T between the principalsurface 11 of the substrate 10 and the Fresnel lens 32.

Since the principal surface 11 is formed as a mirror surface, straylight is prevented from being caused by scattering of the excitationlight EL on the principal surface 11. For this reason, it is possible toprevent the detection accuracy of the particle detector 1 from beingreduced by the stray light as noise. When the principal surface 11 is amirror surface, little scattering light is produced at reflection of theexcitation light EL on the principal surface 11. Hence, interference dueto stray light can be avoided by preventing only the reflected light RL,which is obtained from regular reflection of the excitation light EL bythe principal surface 11, from being mixed into the light receivingoptical system 30. It is difficult to separate scattering light, whichhas low directivity and is uniformly produced, by setting the opticalpath, and when scattering light occurs, it is necessary to use anexpensive filter. In this embodiment, however, the occurrence ofscattering light can be prevented, it is unnecessary to set a filter.This achieves reduction in size and cost of the apparatus.

Particles 100 are collected in the excitation-light irradiation region104. The particles 100 include biogenic particles 101 such asmicroorganisms, and non-biogenic dust 102 such as lint of chemicalfiber. In FIG. 5, an arrow denoted by symbol F represents fluorescenceemitted from the particles 100. Fluorescence F is emitted in alldirections from portions of surfaces of the particles 100 irradiatedwith excitation light EL. Fluorescence F traveling toward the lightreceiving optical system 30 is collected through the Fresnel lens 32,and is received by the light receiving element 34. By using the Fresnellens 32 as the light collecting lens for collecting the fluorescence F,the thickness of the light collecting lens can be reduced. This achievesreduction in size and weight of the particle detector 1.

The fluorescence F is emitted in all directions with no directivity fromthe particles 100 irradiated with the excitation light EL. Part of thefluorescence F directly travels from the particles 100 toward theFresnel lens 32, and another part of the fluorescence F is emitted fromthe particles 100 toward the principal surface 11 of the substrate 10.When the principal surface 11 is a mirror surface, the fluorescence F isspecularly reflected by the principal surface 11, and the reflectedfluorescence F travels toward the Fresnel lens 32. Hence, the intensityof the fluorescence F collected by the Fresnel lens 32 and received bythe light receiving element 34 can be increased. This can improve thedetection sensitivity of the light receiving element 34 to thefluorescence F.

When the Fresnel lens 32 is disposed at a position at the distance Tfrom the principal surface 11 of the substrate 10, the excitation lightEL traveling toward the principal surface 11 of the substrate 10 and thereflected light RL reflected by the principal surface 11 do not enterthe Fresnel lens 32. Light that enters the Fresnel lens 32 is limited toonly fluorescence F emitted from the particles 100, and neither theexcitation light EL nor the reflected light RL is collected by theFresnel lens 32. The light receiving optical system 30 is disposed at aposition such that the excitation light EL and the reflected light RL donot enter the Fresnel lens 32 and the light receiving element 34 doesnot receive the excitation light EL and the reflected light RL. By doingthis, the excitation light EL and the reflected light RL can be reliablyseparated from the fluorescence F, and the excitation light EL or thereflected light RL can be prevented from becoming noise in detection ofthe fluorescence F. Hence, the detection sensitivity to the fluorescenceF can be improved.

FIG. 7 schematically illustrates a cross section of the Fresnel lens 32.The Fresnel lens 32 is formed of a material containing a matrix 32 a andabsorbent 32 b finely dispersed in the matrix 32 a. The matrix 32 a isformed of an arbitrary material that can be used as the Fresnel lens 32,and for example, may be formed of an acrylic material or a glassmaterial that transmits fluorescence F. The absorbent 32 b absorbs alight beam including a wavelength of excitation light EL. The absorbent32 b prevents the light beam including the wavelength of the excitationlight EL from passing through the Fresnel lens 32. The Fresnel lens 32has a filtering function for cutting off the excitation light EL and thereflected light RL.

FIG. 8 is a graph showing filter characteristics of the absorbent 32 b.The horizontal axis in the graph of FIG. 8 indicates the wavelength oflight. The unit of the wavelength is nm. The vertical axis in the graphof FIG. 8 indicates the transmittance of the filter and the spectralintensity of light. The unit of transmittance of the filter is %. Thespectral intensity of light refers to the relative value of spectralintensity at each wavelength when the wavelength such that the spectralintensity of excitation light EL or fluorescence F becomes the highestis 100. In FIG. 8, curve (1) shows the filter characteristics, curve (2)shows the spectral intensity of excitation light EL from thesemiconductor laser element, and curve (3) shows the spectral intensityof fluorescence F emitted from Penicillium irradiated with theexcitation light EL.

According to the filter characteristics shown by curve (1), theabsorbent 32 b has the property of cutting off most of light with awavelength of about 440 nm or less and transmitting most of light with awavelength of about 500 nm or more. The absorbent 32 b has the propertyas a highpass filter (or a low-cut filter) for cutting off light with awavelength of a predetermined threshold value or less and transmittinglight with a wavelength of the threshold value or more.

As shown by curve (2), excitation light EL from the semiconductor laserhas the peak value of optical spectral intensity at a wavelength ofabout 400 nm, and the spectrum is not measured in the other wavelengthranges. In contrast, as shown by curve (3), the spectrum of fluorescenceF from Penicillium is measured in a wavelength range more than or equalto about 460 nm, and the fluorescence F has the peak value of opticalspectral intensity at a wavelength of about 530 nm.

Since the absorbent 32 b having the filter characteristics shown bycurve (1) is dispersed in the Fresnel lens 32, when excitation light ELhaving the optical spectral intensity shown by curve (2) enters theFresnel lens 32, it is absorbed and cut off by the absorbent 32 b. Incontrast, when the fluorescence F having the optical spectral intensityshown by curve (3) enters the Fresnel lens 32, it passes through theFresnel lens 32 while mostly maintaining the optical spectral intensity.

By providing the Fresnel lens 32 with such a filter function, even ifthe excitation light EL or the reflected light RL erroneously enters theFresnel lens 32, it can be cut off by the Fresnel lens 32. Thus, since astructure in which fluorescence F selectively passes through the Fresnellens 32 is provided, noise is prevented from entering the lightreceiving element 34 for detecting the fluorescence F, and the detectionsensitivity to the fluorescence F can be improved. Since the Fresnellens 32 itself has the filter function, it is unnecessary to provide afilter separate from the Fresnel lens 32, and the structure can besimplified and is made inexpensive.

FIG. 9 schematically illustrates radiation characteristics of lightemitted from the semiconductor laser element. The semiconductor laserelement serving as the light emitting element 21 of the embodiment is ofan edge-emitting type having a multilayer structure including a lightemitting layer. The semiconductor laser element is formed by stacking asubstrate 214 formed of n-type GaAs, a lower cladding layer 212 formedof n-type AlGaInP, an active layer 211 formed by a multiquantum well, anupper cladding layer 213 formed of p-type AlGaInP, and a contact layer216 formed of p-type GaAs. The lower cladding layer 212, the activelayer 211, and the upper cladding layer 213 constitute a multilayerstructure 210. A stacking direction of the semiconductor layers thatconstitute the multilayer structure 210 is shown by a two-headed arrowdenoted by symbol LD in FIG. 9.

The semiconductor laser element further includes an n-type electrode 215provided on the substrate 214, a p-type electrode 217 provided on thecontact layer 216, a ridge stripe 218, and current block layers 219formed of n-type AlInP. The ridge stripe 218 and the current blocklayers 219 are disposed between the multilayer structure 210 and thecontact layer 216.

A light emitting part 220 from which excitation light EL is emittedincludes the active layer 211. The light emitting part 220 is longsideways on a light emitting surface of the semiconductor laser element.For example, the light emitting part 220 can be formed such that a ratioobtained by dividing the dimension of the light emitting part 220 in thewidth direction orthogonal to the stacking direction LD by the thicknessof the active layer 211 is 50 or more. The semiconductor laser elementincluding such a striped light emitting part 220 constitutes a so-calledbroad area (BA) semiconductor laser.

In the BA semiconductor laser element, the light emitting part 220 islong sideways, and has a narrow space in a vertical direction. Hence,light emitted from the light emitting part 220 spreads while bendingaround owing to a diffraction effect. For this reason, emittedexcitation light EL spreads such that a spread in the stacking directionLD of the multilayer structure 210 of the semiconductor layers is morethan a spread in the width direction orthogonal to the stackingdirection LD. Owing to the above-described light diffraction effect, theradiation characteristic of the excitation light EL emitted from the BAsemiconductor laser element is band-shaped such that the spread angle ofthe excitation light EL is large in the stacking direction LD of thesemiconductor layers but is small in the width direction orthogonal tothe stacking direction.

That is, the radiation characteristic of excitation light EL emittedfrom the edge-emitting semiconductor laser element is shaped like a bandthat extends long in the stacking direction LD of the multilayerstructure 210 of the semiconductor layers. The excitation light ELemitted from the semiconductor laser element has the property ofspreading comparatively wide in the stacking direction LD of thesemiconductor layers and spreading comparatively narrow in the widthdirection. For this reason, the ratio obtained by dividing the dimensionof the excitation light EL in the stacking direction LD of thesemiconductor layers by the dimension of the excitation light EL in thewidth direction on a plane parallel to the light emitting surface of thesemiconductor layer element increases as the light beam travels awayfrom the semiconductor laser element. Accordingly, the semiconductorlaser element is disposed such the band-shaped excitation light EL formsan excitation-light irradiation region 104 of the optimal shape on theprincipal surface 11 of the substrate 10.

FIG. 10 schematically illustrates an arrangement of the semiconductorlaser element based on the radiation characteristics of laser light. Asillustrated in FIG. 10, the light emitting element 21 formed by thesemiconductor laser element having the multilayer structure 210 of thesemiconductor layers, which includes the active layer 211 serving as alight emitting layer, is disposed such that the stacking direction LD ofthe semiconductor layers extends in the extending direction of theprincipal surface 11 and the stacking direction LD is parallel to theprincipal surface 11 of the substrate 10.

By thus arranging the BA semiconductor laser element, the lightlongitudinal direction in which the excitation light EL emitted from thesemiconductor laser element spreads in a band form can be made parallelto the principal surface 11 of the substrate 10. The excitation light ELis applied onto the principal surface 11 of the substrate 10 in adirection at an angle to the principal surface 11, and the excitationlight EL spreading in the band form is thereby spread in a lateraldirection of the band on the principal surface 11 of the substrate 10.The excitation light EL is applied to the principal surface 11 such thatthe spread in the longitudinal direction and the spread in the lateraldirection are substantially equal, and forms an excitation-lightirradiation region 104 of a symmetrical shape.

For example, the semiconductor laser element, which emits excitationlight EL schematically spreading in an oval shape in FIGS. 9 and 10, isdisposed such that the stacking direction LD of the semiconductor layersis parallel to the principal surface 11 of the substrate 10. Since theexcitation light EL is thereby spread in the lateral direction of theoval on the principal surface 11 of the substrate 10, theexcitation-light irradiation region 104 formed on the principal surface11 is shaped like a substantially perfect circle. For this reason, thearea of the excitation-light irradiation region 104 can be reduced, andthe density of the excitation light EL applied to particles 100collected on the principal surface 11 can be increased. Therefore, theintensity of fluorescence F emitted from the particles 100 can beincreased, and the detection accuracy of the light receiving element 34to the fluorescence F can be improved. This allows the number ofparticles 100 to be detected with high sensitivity.

Preferably, the excitation light EL is applied onto an area on theprincipal surface 11 that extends to some degree so as to form anexcitation-light irradiation region 104 having a predetermined area. Byforming the excitation-light irradiation region 104 that extended on theprincipal surface 11, the excitation light EL can be applied to moreparticles 100 of the particles 100 collected on the principal surface 11of the substrate 10. Hence, the detection accuracy of the particles canbe improved. In contrast, when the excitation light EL is applied to anarea outside the principal surface 11 of the substrate 10, it scattersand becomes stray light. This stray light decreases the detectionaccuracy of fluorescence F. To prevent the occurrence of such straylight, it is necessary to apply all of the excitation light EL onto thesubstrate 10. In this case, if the excitation-light irradiation region104 extends wide, the substrate 10 needs to be increased in size. Thisincreases the size of the particle detector 1.

Accordingly, as illustrated in FIG. 10, when the excitation light EL ismade circular on the principal surface 11 of the substrate 10 to form acircular excitation-light irradiation region 104, a decrease indetection accuracy of the fluorescence F can be prevented, and anincrease in size of the apparatus can be suppressed. Hence, it ispossible to provide a particle detector 1 that has high detectionaccuracy and is suitable for size reduction.

FIGS. 11 to 13 schematically illustrate the arrangement of the Fresnellens 32 relative to the substrate 10. As illustrated in FIG. 11, when itis assumed that excitation light EL and reflected light RL do not have aspread in the ray direction and have a diameter of about 0, theexcitation light EL is representatively shown by the ray direction OD1,and the reflected light RL is representatively shown by the raydirection OD2. The excitation light EL enters the principal surface 11of the substrate 10 at an incident angle θ. Since the principal surface11 is formed as a mirror surface, the excitation light EL is regularlyreflected by the principal surface 11, and the reflected light RL isreflected at a reflection angle θ equal to the incident angle.

When the diameter of the excitation light EL and the reflected light RLis about 0, the Fresnel lens 32 is formed to have a diameter L₀. Toprevent the excitation light EL whose incident angle is θ and thereflected light RL whose reflection angle is θ from interfering with theFresnel lens 32 having the diameter L₀, the Fresnel lens 32 is disposedat a position at a distance T from the principal surface 11 of thesubstrate 10. In this case, a relationship tan θ=(L₀/2)/T=L₀/2T isestablished.

FIGS. 12 and 13 show conditions where excitation light EL and reflectedlight RL do not interfere with the Fresnel lens 32 disposed at thedistance T from the principal surface 11, similarly to FIG. 11, whenthey have a diameter B. Since the excitation light EL and the reflectedlight RL have spreads in the ray directions OD1 and OD2, respectively,the Fresnel lens 32 is formed to have a diameter L that is less than thediameter L₀ in FIG. 11.

In this case, referring to FIG. 13, when a relationship(B/2)/{(L₀−L)/2}=cos θ is established and arranged so that L₀=B/cos θ+L.When this relational expression is substituted in the above-describedexpression, tan θ=(B/cos θ+L)/2T. After all, the distance T between thesubstrate 10 and the Fresnel lens 32 is represented as a function of theangle θ by T=(B/cos θ+L)/2 tan θ. This distance T refers to the minimumdistance by which the Fresnel lens 32 needs to be disposed to be apartfrom the principal surface 11 of the substrate 10 to preventinterference of the excitation light EL and the reflected light RL withthe Fresnel lens 32 when the Fresnel lens 32 has the diameter L, theexcitation light EL has the diameter B, and the excitation light EL hasthe incident angle θ.

That is, in order for the excitation light EL and the reflected light RLnot to interfere with the Fresnel lens 32, the Fresnel lens 32 isdisposed at a distance more than or equal to the distance T found by theabove expression from the principal surface 11 of the substrate 10. Incontrast, as the distance of the Fresnel lens 32 from the substrate 10decreases, the size of the optical system can decrease, and therefore,the size of the particle detector 1 can decrease. In addition, as thedistance of the Fresnel lens 32 from the particles 100 collected on theprincipal surface 11 of the substrate 10 decreases, the receivingefficiency for fluorescence F emitted from the particles 100 increases,and the detection accuracy of the fluorescence F increases. This isbecause the fluorescence F is emitted in all directions with nodirectivity from the particles 100, and the fluorescence F can bereceived in an increasing angle range as the distance of the Fresnellens 32 to the particles 100 decreases. Therefore, the relative positionbetween the Fresnel lens 32 and the substrate 10 is preferablydetermined such that the relationship T=(B/cos θ+L)/2 tan θ isestablished between the distance T and the angle θ.

By increasing the incident angle θ of the excitation light EL anddecreasing the inclination of the excitation light EL from the principalsurface 11, the distance T found by T=(B/cos θ+L)/2 tan θ is decreased.That is, as the incident angle θ of the excitation light EL increases,the reflected light RL becomes less likely to enter the Fresnel lens 32even when the Fresnel lens 32 is located closer to the substrate 10.Hence, the Fresnel lens 32 can be disposed closer to the substrate 10,and this can further reduce the size of the particle detector 1. Forexample, the incident angle θ is preferably set to be within a range notless than 60°.

However, if the incident angle θ is too large, the ray direction OD1 ofthe excitation light EL approaches the direction parallel to theprincipal surface 11. For this reason, the particles 100 collected at aposition close to the excitation optical system 20 are irradiated withthe excitation light EL, whereas the particles 100 collected at aposition apart from the excitation optical system 20 are hidden by theparticles 100 close to the excitation optical system 20, and are notirradiated with the excitation light EL. In this case, since all of theparticles 100 collected on the substrate 10 do not emit fluorescence F,fluorescence F having an intensity corresponding to the collected numberof particles 100 on the substrate 10 cannot be detected, and thisreduces the detection accuracy of the number of particles. Therefore,for example, the incident angle θ is preferably set to be within a rangenot more than 70°.

[Operation of Particle Detector]

A description will be given of operations for detecting the number ofbiogenic particles 101 with the particle detector 1 having theabove-described configuration. FIG. 14 is a flowchart showing a flow ofoperations of the particle detector 1.

Referring to FIG. 14, first, particles 100 are collected on theprincipal surface 11 of the substrate 10 (S101). At this time, air isintroduced into the cabinet of the particle detector 1 through theintroducing portion 3 by driving the fan 92 in a forward direction toform an airflow traveling toward the principal surface 11 of thesubstrate 10. In addition, the electrostatic probe 62 is positionedopposed to the principal surface 11 of the substrate 10, and a potentialdifference is produced between the electrostatic probe 62 and thesubstrate 10 by the collection power-supply circuit 61. Particles 100suspended in the air are thereby charged, and the charged particles 100are collected onto the principal surface 11 of the substrate 10 byelectrostatic force.

Next, the excitation optical system 20 applies excitation light EL tothe particles 100 collected on the substrate 10, and the light receivingoptical system 30 receives fluorescence F emitted from the particles 100upon irradiation with the excitation light EL. The light emittingelement 21 formed by the semiconductor laser element applies excitationlight EL to the particles 100, and the light receiving element 34receives fluorescence F emitted from the particles 100 at this time viathe Fresnel lens 32. The fluorescence intensity before heating of theparticles 100 collected on the substrate 10 is thereby measured (S102).

Next, the particles 100 collected on the substrate 10 are heated byenergizing the heater 91 (S103). Next, energization of the heater 91 isstopped, and the substrate 10 is cooled (S104). At this time, air isintroduced into the cabinet of the particle detector 1 through the fan92 to promote cooling of the substrate 10 by driving the fan 92 in areverse direction.

Next, the excitation optical system 20 applies excitation light EL ontothe particles 100 collected on the substrate 10, and the light receivingoptical system 30 receives fluorescence F emitted from the particles 100upon irradiation with the excitation light EL. The fluorescenceintensity after heating of the particles 100 collected on the substrate10 is thereby measured (S105). By comparing the intensity of thefluorescence F before heating and the intensity of the fluorescence Fafter heating, the number of biogenic particles 101 included in theparticles 100 collected on the substrate 10 is calculated (S106).

FIG. 15 shows a time change of a fluorescence spectrum of Penicilliumbefore and after heat treatment. FIG. 15 shows measurement results ofthe fluorescence spectrum before heat treatment (curve C1) and afterheat treatment (curve C2) when Penicillium is heated as examples ofbiogenic particles 101 at 200° C. for five minutes. These results showthat the intensity of fluorescence from the Penicillium is greatlyincreased by conducting heat treatment.

FIG. 16 shows a fluorescence spectrum of fluorescence-emitting dustbefore heat treatment. FIG. 17 shows a fluorescence spectrum of thefluorescence-emitting dust after heat treatment. FIG. 16 and FIG. 17show measurement results of the fluorescent spectrum before heattreatment (curve C3) and after heat treatment (curve C4), respectively,when the fluorescence-emitting dust is heated at 200° C. for fiveminutes. It is verified that the fluorescence spectrum shown by curve C3and the fluorescence spectrum shown by curve C4 are nearly aligned witheach other. That is, it is known that the intensity of fluorescence fromthe dust does not change before and after heat treatment.

When the biogenic particles 101 suspended in the air are irradiated withultraviolet light or blue light, they emit fluorescence F. However, dust102 that similarly emits fluorescence, such as lint of chemical fiber,is suspended in the air. Hence, when only the fluorescence F isdetected, it is not determined whether the fluorescence F is emittedfrom the biogenic particles 101 or the dust 102.

On the other hand, when the biogenic particles 101 and the dust 102 aresubjected to heat treatment and changes in the fluorescence intensity(fluorescent amount) before and after heating are measured, theintensity of fluorescence emitted from the dust 102 is not changed byheat treatment, whereas the intensity of fluorescence emitted from thebiogenic particles 101 is increased by heat treatment. In the particledetector 1 of the embodiment, the fluorescence intensity of theparticles 100, in which the biogenic particles 101 and the dust 102 aremixed, is measured before and after heating, and a difference betweenthe measured fluorescence intensities is found to specify the number ofbiogenic particles 101.

The intensity of fluorescence F emitted from the biogenic particles 101is increased by heat treatment. For this reason, in Step (S105), afluorescence intensity higher than the fluorescence intensity measuredbefore heating in Step (S102) is measured. An increase amount influorescence intensity is calculated from the difference between thefluorescence intensity before heating and the fluorescence intensityafter heating. On the basis of a prepared relationship between theincrease amount in fluorescence intensity and the concentration ofbiogenic particles, the concentration of biogenic particles 101corresponding to the calculated increase amount can be specified. Thecorrespondence relationship between the increase amount and theconcentration of biogenic particles is experimentally determinedbeforehand.

[Configuration of Particle Removing Apparatus]

The particle detector 1 of the embodiment may be used alone as anapparatus for detecting biogenic particles 101, or may be incorporatedin home electric appliances such as an air purifier, an air conditioner,a humidifier, a dehumidifier, a vacuum cleaner, a refrigerator, and atelevision. FIG. 18 illustrates an exemplary appearance of an airpurifier 300 including the particle detector 1. The air purifier 300 isan example of a particle removing apparatus that efficiently removesbiogenic particles 101 detected by the particle detector 1.

The air purifier 300 includes a switch 310 that receives operationinstructions, and a display panel 330 that displays detection resultsand the like. The air purifier 300 also includes other unillustratedelements such as a suction opening through which air is introduced andan exhaust opening through which air is exhausted. The air purifier 300further includes a communication unit 350 in which a recording medium isloaded. The communication unit 350 may provide connection to acommunication line for communicating with other apparatuses through theInternet. Alternatively, the communication unit 350 may communicate withother apparatuses, for example, through infrared communication orthrough the Internet. The particle detector 1 is disposed in a housingof the air purifier 300. The air purifier 300 can efficiently purifyambient air by virtue of the particle detector 1 that can accuratelydetect biogenic particles 101 and can achieve size reduction.

FIG. 19 is a block diagram of an exemplary functional configuration ofthe air purifier 300. FIG. 19 illustrates an example in which thefunctions of a signal processing unit 50 are implemented by hardwareconfiguration mainly of electric circuitry. However, at least part ofthese functions may be implemented by software configuration realized byan unillustrated CPU (Central Processing Unit) included in the signalprocessing unit 50 to execute a predetermined program. Further, FIG. 19illustrates an example in which a measuring unit 40 is implemented bysoftware configuration. However, at least part of the functions may berealized by hardware configuration such as electric circuitry.

Referring to FIG. 19, the signal processing unit 50 includes acurrent-voltage converting circuit 54 connected to the light receivingelement 34, and an integrating amplifying circuit 55 connected to thecurrent-voltage converting circuit 54.

The measuring unit 40 includes a control unit 41, a storage unit 42, anda clock generating unit 43. The measuring unit 40 further includes aninput unit 44 that receives information input by receiving an inputsignal from a switch 310 upon operation of the switch 310, a displayunit 45 that executes processing for displaying, for example,measurement results on the display panel 330, an external connectionunit 46 that executes processing necessary for exchanging data and thelike with an external apparatus connected to the communication unit 350,and a driving unit 48 that drives the fan 92 and the heater 91.

When particles 100 collected on the principal surface 11 of thesubstrate 10 are irradiated with excitation light EL from the lightemitting element 21, fluorescence F from the particles 100 in theexcitation-light irradiation region 104 is collected at the lightreceiving element 34. The light receiving element 34 outputs a currentsignal in accordance with the amount of received light to the signalprocessing unit 50. The current signal is input to the current-voltageconverting circuit 54.

The current-voltage converting circuit 54 detects a peak current valueH, which represents the fluorescence intensity, from the current signalinput from the light receiving element 34, and converts the peak currentvalue H into a voltage value Eh. The voltage value Eh is amplified by apreset gain by the amplifying circuit 55, and is output to the measuringunit 40. The control unit 41 of the measuring unit 40 receives the inputof the voltage value Eh from the signal processing unit 50, and storesthe input in the storage unit 42 in order.

The clock generating unit 43 generates and outputs clock signals to thecontrol unit 41. With the timing based on the clock signals, the controlunit 41 outputs control signals for rotating the fan 92 to the drivingunit 48, and controls introduction of air by the fan 92. Further, thecontrol unit 41 is electrically connected to the light emitting element21 and the light receiving element 34, and controls ON/OFF of theseelements.

The control unit 41 includes a calculation unit 411. The calculationunit 411 performs operation for calculating the number of biogenicparticles in the introduced air by using the voltage value Eh stored inthe storage unit 42.

The concentration of the biogenic particles 101 in the collectedparticles 100, which is calculated by the calculation unit 411, isoutput from the control unit 41 to the display unit 45. The display unit45 performs processing for displaying the input concentration ofmicroorganisms on the display panel 330. For example, the display panel330 has lamps corresponding to concentrations, and the display unit 45specifies a lamp corresponding to the calculated concentration as a lampto be lighted, and lights the lamp. As another example, a lamp may belighted in different colors according to the calculated concentration.The display on the display panel 330 is not limited to lamp display.Numerical values, concentrations, or messages prepared beforehandcorresponding to the concentrations may be displayed. The measurementresults may be written on a recording medium loaded in the communicationunit 350 or may be transmitted to an external apparatus via thecommunication unit 350 by the external connection unit 46.

The input unit 44 may receive selection of a display method on thedisplay panel 330 according to an operation signal from the switch 310.Alternatively, the input unit 44 may receive selection of display of themeasurement results on the display panel 330 or output of themeasurement results to the external apparatus. A signal indicating thecontents of selection is output to the control unit 41, and the controlunit 41 outputs a necessary control signal to the display unit 45 and/orthe external connection unit 46.

The particle detector 1 utilizes the difference in characteristicsbetween fluorescence F from the biogenic particles 101 and fluorescenceF from the dust 102 for emitting the fluorescence F due to heattreatment, and detects biogenic particles 101 on the basis of anincrease amount after predetermined heat treatment. For this reason,even when dust 102 for emitting fluorescence F is contained in theintroduced air, the particle detector 1 accurately detects biogenicparticles 101 separate from the dust 102 for emitting fluorescence on areal-time basis.

The air purifier 300 utilizes the concentration of biogenic particles101 detected by the particle detector 1, and can efficiently remove thebiogenic particles 101 by changing the operating state according to theoutput from the particle detector 1. That is, when the output of theparticle detector 1 is large and the concentration of biogenic particles101 is high, a particle removing ability of the air purifier 300 can beenhanced, for example, by rotating the fan 92 at high speed to increasethe ventilation amount. When the output of the particle detector 1 issmall and the concentration of biogenic particles 101 is low, theparticle removing ability can be reduced. Hence, the rotation number ofthe fan 92 is decreased to reduce the ventilation amount, andpower-saving operation can be achieved.

Although the embodiment of the present invention has been describedabove, it should be considered that the disclosed embodiment is notrestrictive, but is illustrative in all respects. The scope of thepresent invention is defined by the claims, not by the abovedescription. Further, the scope of the present invention is intended toinclude all modifications within the meaning and range equivalent to thescope of the claims.

INDUSTRIAL APPLICABILITY

The present invention is used as an apparatus that mainly detectsbiogenic particles such as pollen, microorganisms, and mold.

REFERENCE SIGNS LIST

1 particle detector

10 substrate

11 principal surface

20 excitation optical system

21 light emitting element

24 light collecting lens

30 light receiving optical system

32 Fresnel lens

32 a matrix

32 b absorbent

34 light receiving element

100 particle

101 biogenic particle

102 dust

104 excitation-light irradiation region

210 multilayer structure

211 active layer

220 light emitting unit

300 air purifier

A optical axis

B diameter of light

EL excitation light

F fluorescence

L, L₀ diameter of lens

LD stacking direction

OD1, OD2 ray direction

RL reflected light

T distance

θ incident angle.

The invention claimed is:
 1. A particle detector that detects biogenic particles, comprising: a collecting member having a principal surface and configured to collect the biogenic particles on the principal surface; a light irradiation unit configured to irradiate the particles collected on the principal surface with excitation light emitted from the light irradiation unit in a direction which defines an acute angle relative to the principal surface; and a light receiving unit configured to receive fluorescence emitted from the particles when the particles are irradiated with the excitation light from the light irradiation unit, wherein an optical axis of the light receiving unit and a ray direction of the excitation light intersect with each other, wherein the principal surface is a mirror surface, wherein the light irradiation unit includes an edge-emitting semiconductor laser element, and wherein the semiconductor laser element has a multilayer structure including a light emitting layer, and is disposed such that a stacking direction of the multilayer structure is parallel to the principal surface. 